Combat over planet, do not bomb it away

[Jubala]

How do I get my fleet to kill all ships and weapon platforms but not the facilities and population in strategic combat (sim turn game)? I want my ships to stop shooting at the planet as soon as it can't shoot back so I can invade it when the troops arrive. I can give them orders not to fire at planets in the strategy of the fleet, but that will leave the weapon platforms on the planet (I think).